The present invention relates to stabilized hydroxylamine solutions comprising at least one compound of the formula (I) or (II) as stabilizer, to the use of compounds of the formula (I) or (II) as stabilizer in hydroxylamine solutions, and to methods of stabilizing hydroxylamine solutions.
The present invention further relates to tri(4-(2,3-dihydroxyphenyl)-4-keto-3-azabutyl)amine of the formula 
Basic or neutral solutions comprising hydroxylamine in the form of the free base enjoy numerous applications, for example, in the synthesis of fine chemicals or in the electronics industry.
It is known that such solutions are unstable and undergo decomposition to ammonia, nitrogen, nitrogen oxides, and water, so that transport and storage of such solutions is problematic.
In order to retard the decomposition, a stabilizer is added to the solutions. Stabilizers already proposed include the following:
thioglycolic acid (JP-A-58069843), glycerol monoethers and ethylene oxide adducts thereof (DE-A-2919554), hydroxyanthraquinones (DE-A-3343600), hydroxyquinolines (DE-A-3345734), polyhydroxyhexano-1,4-lactone (DE-A-3345733), anthocyanins (DE-A-3347260), hydroxyquinaldines, flavones, benzonitrile, N-phenyl-N-hydroxythiourea (DE-A-3601803), flavans (DE-A-3343599), thiosulfates, mercaptobenzothiazoles, mercaptoalkanols, mercaptothiazolines, thiuram disulfides, thioureas (EP-A-516933), the tetrasodium salt of ethylenediaminetetraacetic acid, the trisodium salt of N-hydroxyethylethylenediaminotriacetic acid, polyvinylpyrrolidone or poly-N-vinyl-5-ethyl-2-oxazolidinone (U.S. Pat. No. 3,145,082), amide oximes (U.S. Pat. No. 3,480,391), hydroxamic acids (U.S. Pat. No. 3,480,391), hydroxyureas (U.S. Pat. No. 3,544,270), dipyridyl compounds (JP-A-58069842), aminoquinolines (JP-A-58069844), phenanthrolines (JP-A-58069841), and polyhydroxyphenols (JP-A-4878099).
A disadvantage of these stabilizers is that they do not stabilize a hydroxylamine solution sufficiently for prolonged storage.
As a stabilizer which permits longer storage of a hydroxylamine solution, DE-A-19 547 759 proposed trans-1,2-diaminocyclohexane-N,N,Nxe2x80x2,Nxe2x80x2-tetraacetic acid.
Although this stabilizer permits a longer storage period than those mentioned above, there is a further need for a prolongation of the possible storage period of hydroxylamine solutions.
It is an object of the present invention to provide a stabilizer for hydroxylamine solutions which permits a better possibility of stabilization, especially long-term stabilization, of hydroxylamine solutions.
We have found that this object is achieved by the stabilized hydroxylamine solutions defined at the outset, comprising at least one compound of the formula (I) or (II) as stabilizer, the use of compounds of the formula (I) or (II) as stabilizers in hydroxylamine solutions, methods of stabilizing hydroxylamine solutions and compounds of the formula (II).
The compounds of the formula (I) or (II) may be used as they are in the form of salts with organic acids, such as formic acid, acetic acid, benzoic acid, or, preferably, inorganic acids, such as sulfuric acid, nitric acid, phosphoric acid, phosphorous acid, preferably a hydrohalic acid, especially hydrogen chloride or hydrogen bromide.
Suitable compounds in accordance with the invention are tri(4-(2,3-dihydroxyphenyl)-4-oxabutyl)amine of the formula 
and tri(4-(1,2-dihydroxyphenyl)-4-keto-3-azabutyl)amine of the formula 
and also the salts thereof, preferably with hydrogen halide, especially hydrogen chloride or hydrogen bromide, such as
tri(4-(1,2-dihydroxyphenyl)-4-keto-3-azabutyl)amine hydrochloride,
tri(4-(1,2-dihydroxyphenyl)-4-keto-3-azabutyl)amine hydrobromide,
tri(4-(1,2-dihydroxyphenyl)-4-oxabutyl)amine hydrochloride, and
tri(4-(1,2-dihydroxyphenyl)-4-oxabutyl)amine hydrobromide.
The stabilized hydroxylamine solutions of the invention comprise at least one, such as 1, 2, 3 or 4, preferably 1 or 2, especially 1, compound of the formula (I) or (II) in free form or in the form of one or more at least partly neutralized salts; i.e., free compound of the formula (I) or (II) is present in the mixture with one or more salts of one or more compounds of the formula (I) or (II) in the mixture as the stabilizer. Similarly, the stabilized hydroxylamine solutions of the invention may comprise at least one, such as 1, 2, 3 or 4, preferably 1 or 2, especially 1, compound of the formula (I) or (II) in the form of one or more fully neutralized salts.
The stabilized hydroxylamine solutions of the invention comprise hydroxylamine in the form of the free base or an at least partly neutralized hydroxylamine salt; i.e., free hydroxylamine is present in a mixture with the hydroxylamine salt.
The stabilizers employed in accordance with the invention may be used to stabilize all kinds of hydroxylamine solutions. They may be aqueous solutions or solutions of hydroxylamine in an organic solvent, such as methanol, ethanol, n-propanol, isopropanol, acetone, tetrahydrofuran, etc., or mixtures of water and organic solvents. The stabilizers employed in accordance with the invention are likewise soluble in the solvents in which hydroxylamine is soluble.
Hydroxylamine solutions are generally obtained by reacting a hydroxylammonium salt, especially hydroxylammonium sulfate, hydroxylammonium chloride and hydroxylammonium phosphate, with an appropriate base, such as ammonia, sodium hydroxide, potassium hydroxide or calcium hydroxide. In the case of full neutralization of the hydroxylammonium salt a solution is obtained which contains free hydroxylamine and the salt originating from the base cation and the acid anion present in the hydroxylammonium salt. Some or all of the salt may be separated off. The hydroxylammonium salt may also be neutralized only partly with the base. In that case a solution is obtained which contains not only free hydroxylamine and the above-mentioned salt but also unreacted hydroxylammonium salt. All these solutions may be stabilized in accordance with the invention, the nature of the anion in the hydroxylammonium salt being uncritical.
The stabilized hydroxylamine solutions of the invention comprise the compounds of the formula (I) or (II) in an amount sufficient for stabilization. They preferably contain from 0.001 to 20% by weight (from 10 to 200,000 ppm), in particular 0.001 to 10% by weight, with particular preference from 0.01 to 5% by weight, with very particular preference from 0.02 to 2% by weight, of compound of the formula (I) or (II), based on the hydroxylamine content. The hydroxylamine concentration is generally from 1 to 100% by weight, in particular from 1 to 70% by weight, based on the overall weight of the solution.
The stabilizer may be added before or after neutralization of the hydroxylamine salt, but preferably before neutralization.
The compounds of the formula (I) or (II) are effective within a wide temperature range. Thus they stabilize hydroxylamine solutions in the range from xe2x88x9220xc2x0 C. to 130xc2x0 C., preferably from xe2x88x9210xc2x0 C. to 100xc2x0 C. However, they are also suitable as stabilizers even at markedly higher temperatures under the pressures required to liquefy the solution.
The examples below illustrate the invention without restricting it. The hydroxylamine concentrations reported in the examples are determined by redox titration.